(A) Field of the Invention
The present invention relates to an integrated circuit (IC) assembly method, and more specifically, to an IC assembly method regarding wafer-level packaging.
(B) Description of Related Art
Wafer-Level Packaging (WLP) refers to the technology of packaging an integrated circuit at wafer level, instead of the traditional process of assembling the package of each individual unit after wafer dicing. WLP is essentially a true chip-scale packaging (CSP) technology, since the resulting package is practically of the same size as the die. Furthermore, wafer-level packaging paves the way for true integration of wafer fab, packaging, test, and burn-in at wafer level, for the ultimate streamlining of the manufacturing process undergone by a device from the start to customer shipment.
Wafer-level packaging basically consists of extending the wafer fab processes to include device interconnection and device protection processes. However, there is no single industry-standard method of doing this at present. Generally, there are many WLP technology classifications in existence today.
Encapsulated Copper Post technology is one of the WLP technologies. The chip's bond pads are also rerouted into an area array of interconnection points. In this technology, however, the interconnection points are in the form of electroplated copper posts, instead of pads.
These copper posts provide enough stand-off for the active wafer surface to be encapsulated in low-stress epoxy by transfer molding, exposing only the top portions of the posts for bonding.
The conventional copper-to-copper post bonding uses thermal bonding technology like hot press, in which the key factors include temperature, time and pressure. As shown in FIGS. 1 and 2, the dies 11 with copper posts 12 are placed upside down, and the copper posts 12 are aligned with the copper posts 13 of a mother device wafer 14. The copper posts 12 and 13 are bonded together in an environment of a temperature higher than the melting point of copper by solid state diffusion. However, the melting point of copper is very high (greater than 1000° C.), and therefore, bonding takes a long time. As usual, it takes around 20 to 30 seconds for each die bonding. In addition, the breakage of wafers or dies may occur due to compression of bonding, and high yield loss may occur due to copper-to-copper post misalignment. Another shortcoming is that the process is very costly because the equipment is complicated and expensive.